The first GSM (Global System for Mobile communication) networks were designed for voice services. When the use of GSM data services began, it became evident that the Circuit Switched (CS) bearer services were not particularly well-suited for certain types of applications with a bursty nature. Therefore, the new Packet Switched (PS) data transmission service GPRS (General Packet Radio Service) was defined for packet services. GPRS is a packet radio network utilising the GSM network, which endeavours to optimize data packet transmission by means of GPRS protocol layers on the air interface between a mobile device (e.g. a mobile station) and a GPRS network.
A GPRS mobile device (MS) can operate in one of three modes of operation: class A, class B, and class C modes of operation. See, for example, 3GPP TS 23.060, “Service description; Stage 2” which is incorporated herein by reference. In the class A mode of operation, the MS is attached to both GPRS and other GSM services. The mobile user can make and/or receive calls on the two services simultaneously, for example having a normal GSM voice call and receiving GPRS data packets at the same time. In class B mode of operation, the MS is attached to both GPRS and other GSM services, but the MS can only operate one set of services at a time. In class C mode of operation, the MS can only be attached either to the GSM network or the GPRS network. The selection is done manually and there are no simultaneous operations.
A problem occurs with MS behavior when the MS operates in the class A mode (i.e. dual transfer mode) of operation. According to standards, when the MS releases a CS connection (i.e. an RR connection) while in the Dual Transfer Mode (DTM), packet resources may be aborted. See, for example, 3GPP TS 44.018, “Radio Resource Control Protocol” which is incorporated herein by reference. This problem is separate from the problems encountered when changing from packet transfer mode to dual transfer mode, as discussed in U.S. patent application Ser. No. 10/802,407 filed Mar. 16, 2004 (incorporated herein by reference). This problem is likewise separate from the problems encountered when a mobile device is forced to idle its packet switching capabilities, when transitioning from dual transfer mode to packet transfer mode, as discussed in U.S. patent application Ser. No. 10/763,936 (incorporated herein by reference).
If the network and the MS support an enhanced DTM CS release procedure, the MS may directly enter packet transfer mode when an RR connection has been released. This is illustrated in the FIG. 1. Also see 3GPP TS 43.064, “Overall description of the GPRS radio interface; Stage 2” (incorporated herein by reference).
Based on the current standard (3GPP TS 44.018, “Radio Resource Control Protocol,” incorporated herein by reference), when the MS is in packet transfer mode and a CS connection (also referred to as a radio resource or RR connection) is needed, then all packet resources must first be aborted, then an RR connection is established, and finally packet resources may be requested. This process occurs, for example, when the MS initiates a call.
This prior art system is illustrated in FIG. 1 (also see 3GPP TS 43.064, “Overall description of the GPRS radio interface; Stage 2,” mentioned above), which shows RR operating modes and transitions between Class-A (DTM supported) and Class-B. A Temporary Block Flow (TBF) Release moves the MS from the Packet Transfer Mode 106 into an Idle/Packet Idle state 104, after which the MS must then establish a dedicated RR connection 108 in order to then access dual transfer mode 102 that includes both packet transfer capability and RR capability. In other words, after the release of the packet transfer connection 106, the MS is in the packet idle mode 104 and must perform a complete acquisition of system information and ask for PS resources all over again, in order to get into the Dual Mode 102 via the dedicated CS mode 108.
FIG. 2 illustrates how the prior art system works with the enhanced DTM CS release procedure. The four vertical lines represent portions or stages of the network. The line 202 represents the mobile device (MS), the line 204 represents the base station system (BSS), the line 206 represents the serving GPRS support node (SGSN), and the line 208 represents the mobile switching center (MSC). FIG. 2 shows that initially a circuit switched session 212 and a packet switched session 210 are in progress according to the dual mode. Then, either the MS or the network can initiate a disconnect 213 of the CS connection, which causes the circuit switched call to be released at call control level and subsequently the channel is released. In FIG. 2, the CS=RR connection is released and the MS moves to packet transfer mode 216. The MS can maintain its packet resources only in timeslots used for packet transfer. Therefore, the MS releases a single timeslot allocated only for the RR connection or single timeslot shared with the RR connection and packet transfer. While in packet transfer mode, the network likely reconfigures and increases the number of allocated timeslots for the MS with current procedures specified in 3GPP TS 44.060, “Radio Link Control/Medium Access Control (RLC/MAC) protocol,” mentioned above.
Unfortunately, the present standard does not specify the allocation of timeslots (i.e. the number and location in the TDMA structure is not specified) to be used in packet transfer mode after the release of the RR connection. The current working assumption is that the mobile device could use the packet resource that is used in dual transfer mode, excluding (e.g. the number and location excluding) a possible timeslot shared with the RR connection traffic. However, there is currently no way to flexibly allocate packet resources when the RR connection is released while in dual transfer mode.